The Earth's atmosphere is known to team with airborne microorganisms, though the high light intensities, extreme temperature variations, low concentrations of organic matter and scarcity of water, make the environment unsuitable for microbial growth. Biological material may contribute about 20%, 22% and 10% to the total airborne particulate matter by volume in remote continental, populated continental and remote maritime environments, respectively. Most of them originate from natural sources such as soil, lakes, animals and humans. Moreover, agricultural practices, health care units and industrial operations such as sewage treatment, animal rearing, fermentation processes, and food processing plants also emit viable microorganisms into the environment.
Bacteria form a large domain of single-celled, prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from cocci to rods and spirals. Bacteria are ubiquitous on Earth, growing in soil, acidic hot springs, radioactive waste, water, and deep in the Earth's crust, as well as in organic matter and the live bodies of plants and animals. The bacilli are rod-shaped, gram-positive, sporulating, aerobic or facultative anaerobic bacteria. Most bacilli are saprophytes. Each bacterium creates only one spore, which is resistant to heat, cold, radiation, desiccation, and disinfectants. The bacilli exhibit an array of physiological abilities that allow them to live in a wide range of habitats, including many extreme habitats such as the desert sands, hot springs, and Arctic soils. Bacillus species can be thermophilic, psychrophilic, acidophilus, alkaliphilic, halotolerant, or halophilic and are capable of growing at various pH values, temperatures, and salt concentrations.
Production of antimicrobial agents seems to be a general phenomenon for most bacteria. These bacteria produce an admirable array of microbial defense systems, including broad-spectrum classical antibiotics, metabolic by-products such as organic acids, and lytic agents such as lysozyme. In addition, several types of protein exotoxins, and bacteriocins, which are biologically active peptide moieties with bactericidal mode of action, are also produced. The biological arsenal from microbes is remarkable in its diversity and natural abundance.
The search for new antimicrobial agents is a field of utmost importance. The development of resistance to antimicrobial agents is increasing at an alarming rate. Current solutions involve development of a more rational approach to antibiotic use and discovery of new antimicrobials.
Highly Relevant Patents
                1. Novel bacterial strains and methods of controlling fungal pathogens (WO/2000/015761).        